People spends hours at a time with their electronic devices—computers, telephones, music players, and the like. They like best those devices that are intuitive to use and whose interactions best meet their expectations regarding how machines should work. They interact with electronics through inputs and outputs from the devices, where the outputs generally are provided audibly and/or on a flat graphical display screen, and the inputs may occur via touch screens, joysticks, mice, 4-directional keypads (e.g., d pads), and other such input mechanisms.
Fine distinctions in user interfaces can make a world of difference in a user's experience with a device. Intuitive user interface interactions may be at a premium for mobile devices, where display sizes are generally limited, as are input mechanisms (e.g., full size keyboards may be hard to implement because of space constraints, or may be hard to use when a user cannot easily use both hands with their computing device).